High velocity electrostatic coalescing oil/water separator

ABSTRACT

An apparatus and method for separating water from an oil-and-water mixture includes at least two elongated separator vessels oriented at an incline and connected to one another so that an upwardly flowing oil predominant fluid passes from the first separator vessel to the second separator vessel where further electrostatic separation of water from the oil predominant fluid occurs. Each vessel has an electrode at its upper end preferably connected to a different voltage source. The inlet to each vessel is located relative to the electrode to provide an up flow or a down flow vessel. Additionally, the first vessel may be at a different elevation than the second vessel. An additional vessel may be included with output from the first vessel bypassing the additional vessel, the second vessel, or both. Baffles may be added in the water collection portion of each vessel to reduce turbulence and settling distance.

REFERENCE TO PENDING APPLICATIONS

This application is not based upon any pending domestic or international patent applications.

FIELD OF THE INVENTION

This invention is in the field of electrostatic coalescence of immiscible components of a mixture, and is particularly related to the separation of water from a water-and-oil mixture.

BACKGROUND OF THE INVENTION

One of the world's most useful sources of energy is crude oil, derived from subterranean formations. When crude oil arrives at the earth's surface it is typically in the form of a water-and-oil mixture. That is, crude oil invariably has associated water that must be separated before the oil component can be efficiently refined into useful commercially acceptable products.

A common technique for improving the effectiveness of oil/water separation is by use of coalescence—that is a technique of joining together smaller into larger water droplets that are more readily separated from the mixture. As water droplet size increases, the dynamics of gravitational separation improve. One method of augmenting coalescence of water droplets is by subjecting the mixture to an electric field. Oil, being a non-polar fluid, acts as a dielectric and water droplets, being polar, when subjected to an electric field are coalesced. Coalescence is usually practiced by establishing an electric field between electrodes and passing an oil-in-water mixture through the electric field. Since water is slightly polar, water droplets become polarized by the electric field. Polarized droplets are attracted to each other and move into and coalescence with each other. Larger droplets tend to gravitate downwardly within the mixture and the oil, having portions of the water removed therefrom, tend to gravitate upwardly within the mixture.

Much work has been done in the area of electrostatic coalescence of a mixture to augment separation of oil and water components. Background information relating to the inventive subject matter contained herein can be obtained from the following United States patents:

Pat. No. Inventor Title 1,116,299 Laird et al. Process of treating petroleum emulsions 1,276,387 McKibben Method of separating associated liquids 1,838,931 Fisher Apparatus for converting commercial frequency circuits into high frequency circuits 2,120,932 Dillon High frequency induction dehydrator 2,849,395 Wintermute Method and apparatus for electrical separation of emulsions 3,772,180 Prestridge Electric treater 3,839,176 McCoy Method and apparatus for removing contaminants from liquids 3,847,775 Prestridge Process for electrical coalescing of water 4,126,537 Prestridge Method and apparatus for separation of fluids with an electric field 4,161,439 Warren et al. Apparatus for application of electrostatic fields to mixing and separating fluids 4,200,516 Pope Electrostatic coalescing system 4,204,934 Warren et al. Process for application of electrostatic fields to mixing and separating fluids 4,224,124 Pope Electrostatic coalescing system 4,283,290 Davies Purification utilizing liquid membrane with electrostatic coalescence 4,290,882 Dempsey Electrostatic separation of impurities phase from liquid-liquid extraction 4,308,127 Prestridge Separation of emulsions with electric field 4,400,253 Prestridge Voltage control system for electrostatic oil treater 4,415,426 Hsu et al. Electrodes for electrical coalescence of liquid emulsions 4,417,971 Ferrin et al. Circuit for maintaining the strength of an electrostatic field generated in a fluid mixture of varying dielectric strength 4,469,582 Sublette et al. Electrically enhanced inclined plate separator 4,479,161 Henrich et al. Switching type driver circuit for fuel injector 4,581,119 Rajani et al. Apparatus for separating a dispersed liquid phase from a continuous liquid phase by electrostatic coalescence 4,581,120 Sublette Method and apparatus for separating oilfield emulsions 4,601,834 Bailes et al. Settling of liquid dispersions 4,606,801 Prestridge et al. Electrostatic mixer/separator 4,702,815 Prestridge et al. Distributed charge composition electrodes and desalting system 4,747,921 Bailes Liquid-liquid contacting 4,767,515 Scott et al. Surface area generation and droplet size control in solvent extraction systems utilizing high intensity electric fields 4,804,453 Sublette et al. Resolution of emulsions with multiple electric fields 5,147,045 Chi et al. Particulate separations by electrostatic coalescence 5,411,651 Yamaguchi et al. Method for electrostatic liquid/liquid contactor 5,421,972 Hickey et al. Process and apparatus for removing soluble contaminants from hydrocarbon streams 5,464,522 MacEdmondson Electrostatic oil emulsion treating method and apparatus 5,543,027 Yamaguchi et al. Apparatus for electrostatic liquid/liquid contactor 5,565,078 Sams et al. Apparatus for augmenting the coalescence of water in a water-in-oil emulsion 5,575,896 Sams et al. Method and apparatus for oil/water separation using a dual electrode centrifugal coalescer 5,643,431 Sams et al. Method for augmenting the coalescence of water in a water-in-oil emulsion 5,824,203 Remo Method and means for changing characteristics of substances 6,010,634 Sams et al. System and method for separating mingled heavier and lighter components of a liquid stream 6,113,765 Wagner et al. Methods for enhanced resolution of hydrocarbon continuous emulsions or dispersions with conductivity modifiers 6,860,979 Sams Dual Frequency Electrostatic Coalescence

BRIEF SUMMARY OF THE INVENTION

This invention provides a method and apparatus for separating water from a water-and-oil mixture. The invention is particularly useful for separating water from crude oil. A great deal of the energy consumed on the earth today is derived from crude oil that is found in subterranean deposits and brought to the earth's surface by wells. When the crude oil reaches the earth's surface it invariably is in the form of a water-and-oil mixture. That is, crude oil is usually found associated with water. In order to successfully and economically transport, refine and make use of crude oil, one of the first requirements after the crude oil is brought to the earth's surface is to separate out and properly dispose of the water content. Methods and various systems for accomplishing this are illustrated and described herein.

One embodiment of this invention includes an elongated inlet vessel having a lower outlet end and an upper inlet end. The elongated inlet vessel can typically be in the form of a pipe, the diameter of which will be determined by the quantity of crude oil to be processed. While the pipe is an example of a readily available elongated vessel, the cross-section of the elongated vessel can be square, rectangular or other shape but for all practical purposes a pipe functions completely satisfactory and is readily available and inexpensive.

A second element making up the apparatus of this invention is a separation vessel that has an upper oil outlet, a lower water outlet and an intermediate inlet passageway. As with the inlet vessel, the separation vessel can, by example, be a length of pipe having a circular cross-section and the diameter of the separation vessel can typically be the same or substantially the same as the diameter of the inlet vessel. The separation vessel typically is elongated with respect to the diameter and may typically be about the same in length as the inlet vessel.

At least one electrode is positioned with the inlet vessel by which a mixture flowing therethrough is subjected to an electric field. The electrode may be, as an example, in the form of a coil conductor that receives the voltage applied through an insulator in the wall of the inlet vessel. The voltage may be applied between the electrode and the inlet vessel itself when the inlet vessel is a metallic conductor. The electrode may be insulated or in appropriate applications may be bare, that is in electrical contact with the mixture liquid flowing through the inlet.

The separator functions by providing short liquid flow paths. A mixture, after being subjected to an electric field within an inlet vessel is immediately passed to a separation vessel where passageways are provided for downward flow of separated water and upward flow of oil having a substantial portion of the water extracted therefrom.

The apparatus for separating water from a water-and-oil mixture may be arranged in series relationship whereby the percentage of water removed from the mixture is increased or may be arranged in a parallel relationship to adjust for varying quantities of crude oil being treated.

Another embodiment of this invention includes a first and a second elongated separator vessel both oriented on an incline and connected to one another so that the oil predominant flow exiting the outlet of the first vessel enters the inlet of the second vessel, where it is once again exposed to an electric field. Substantially dry oil then exits the second vessel. The water-and-oil mixture preferably enters the first vessel below the electrode but above the water level control in the lower end or water collection portion of the vessel. At least one of the separator vessels includes a plurality of baffles arranged parallel one another in the water collection portion of the vessel. The baffles may be horizontal, vertical, or, preferably, angled.

The first vessel may be arranged so that it is at the same elevation as that of the second vessel or at a different elevation. The inlet of the first or second vessel may be located below the electrode and above the water level control or it may be located at its upper end, thereby making the vessel a down flow vessel. A pretreatment or degasser unit may be connected to the inlet of the first elongated separator vessel.

The first vessel can run a bare electrode in circuit relationship to an AC voltage source at a lower potential. The ability to use a bare electrode is one advantage of the first vessel being an upflow vessel, the flow being pre-treated in the AC field. The moderate water fraction of the mixture exiting the first vessel and entering the second vessel, which can be an upflow or downflow vessel, allows for the use of an insulated electrode which may be in circuit relationship to a DC voltage source at a higher potential. The voltage source may include reactance. The second vessel could also use a bare electrode when configured as an upflow vessel

A method of separating water from the water-and-oil mixture includes the steps of:

-   -   (a) flowing the water-and-oil mixture into an inlet of a first         elongated separator vessel, the first elongated separator vessel         being oriented on an incline and having an outlet and an         electrode located toward its upper end;     -   (b) passing the mixture through an electric field of the first         elongated separator vessel whereby water in the water-and-oil         mixture coalesces and a first water predominant fluid flows         downward;     -   (c) flowing a portion of the first oil predominant fluid out of         the outlet of the first elongated separator vessel and into an         inlet of a second elongated separator vessel, the second         elongated separator vessel being oriented on an incline and         having an electrode located toward its upper end;     -   (d) passing the portion of the first oil predominant fluid         through an electric field of the second elongated separator         vessel whereby water in the oil predominant fluid coalesces and         a second water predominant fluid flows downward.

The inlet of each separator vessel is preferably arranged relative to the electrode of the vessel to provide for a desired direction of flow, either an up flow or a down flow, for the passing steps (b) and (d). A portion of the first oil predominant fluid flowing out of the outlet of the first elongated separator vessel and into the inlet of a second or third elongated separator vessel may be a wet oil or a medium-wet oil portion. A second portion of the first oil predominant fluid may also be passed through an outlet and along a path which bypasses the second (or other subsequent) elongated separator vessels.

A better understanding of the invention will be obtained from the following detailed description of the preferred embodiments taken in conjunction with the drawings and the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described in further detail. Other features, aspects, and advantages of the present invention will become better understood with regard to the following detailed description, appended claims, and accompanying drawings (which are not to scale) where:

FIG. 1 is an elevational view of a basic system for practicing the essence of the invention.

FIG. 2 is an alternate view of a basic system of the invention herein. FIG. 2 shows a tubular inlet vessel having an electrode therein by which a mixture is subjected to an electrostatic field and divergent water collection and oil collection portions in communication with oil treatment process and water treatment process vessels.

FIG. 3 is another alternate embodiment of the basic concept of the invention wherein the separation vessel is vertical with an upper product outlet and a lower water outlet.

FIG. 4 is an elevational view of an embodiment of the invention showing how basic systems used to practice the invention may be placed in series to achieve greater completeness of separation of water from the mixture. Further, FIG. 4 illustrates an inlet manifold and an outlet manifold that can be used so that the system extending between the manifold may be repeated in parallel to thereby adapt the system for increase volume applications.

FIG. 5 shows a desalter embodiment of the invention wherein a separation system is used in an application for extraction of salt from a mixture.

FIG. 6 shows another desalter system and illustrates how two of the basic separation systems of the invention may be employed in a network to provide more thorough water separation and salt removal.

FIG. 7 is a diagrammatic view showing how the basic arrangement of FIG. 2 may be repeated multiple times as necessary depending upon the level of dehydration required of the system. As an example, FIG. 4 illustrates two basic systems in sequence whereas FIG. 7 shows diagrammatically three basic systems in sequence.

FIG. 8 illustrates another embodiment of the invention wherein the basic separation system of the invention follows an inlet structure particularly useful in extracting gas from the inlet mixture and wherein two basic separation systems, the first like FIG. 2 and the second like FIG. 1, are employed in series.

FIG. 9 illustrates another embodiment of the invention wherein the separation vessel is oriented at about 22.5° relative to horizontal.

FIGS. 10, 11 and 12 provide cross-sectional views of alternate embodiments of the electrode. FIG. 10 illustrates a rod-type electrode configuration. FIG. 11 illustrates a coil-type electrode configuration. FIG. 12 illustrates a plate-type electrode configuration.

FIG. 13 is an alternate embodiment of the basic system for practicing the invention as first disclosed in FIG. 1. This embodiment employs a horizontal transition section between the inlet vessel and the oil collection portion to reduce turbulence where the flow of separated water diverges from the flow of separated oil.

FIG. 14 is an alternate embodiment of a system for separating water from a water-and-oil mixture. Two up flow stages are arranged one above the other, each having the wet oil inlet located below the electrode.

FIGS. 15 to 15B illustrate another alternate embodiment in which two up flow stages are arranged next to (or horizontal with) one another. Similar to the system of FIG. 14, the wet oil inlet to each stage is located below the electrode.

FIG. 16 illustrates the system of FIG. 14 equipped with an optional degasser/pretreatment unit connected to the inlet of the first up flow stage.

FIG. 17 is a partial cross-section view of the water leg portion of each stage of FIG. 15 illustrating a plurality of baffles designed to improve water quality.

FIG. 18 illustrates the system of FIG. 15 equipped with an optional degasser/pretreatment unit connected to the inlet of the first up flow stage.

FIGS. 19 to 21 provide cross-sectional views of various baffle arrangements that may be provided in the water leg portion of the up flow stages of FIGS. 14 and 15.

FIG. 22 is yet another alternate embodiment of a system for separating water from a water-and-oil mixture. The first stage is an up flow stage. The second stage is a down flow stage.

FIG. 23 is a view of the embodiment illustrated in FIG. 22 and taken along section line 23-23 of FIG. 22.

FIG. 24A is another alternate embodiment of a system for separating water from a water-and-oil mixture. Two down flow stages are preceded by degasser/pretreatment unit connected to the inlet of the first down flow stage.

FIG. 24B is an alternate embodiment of the system of FIG. 24A. Because of the relatively low pressure drop experienced across the stages, the separator vessels are plumbed to a single header and controlled with a single level control.

FIG. 25 is a schematic illustrating yet another alternate embodiment of a system made according to this invention for separating water from a water-and-oil mixture. An additional outlet is provided to the first stage which allows oil that is dry enough to meet a user's requirements to bypass the second stage.

FIG. 26 is a schematic illustrating another alternate embodiment in which an additional outlet is provided at the first and second stages to allow dry oil to bypass a subsequent stage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is to be understood that the invention that is now to be described is not limited in its application to the details of the construction and arrangement of the parts illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. The phraseology and terminology employed herein are for purposes of description and not limitation.

Elements shown by the drawings are identified by the following numbers:

10 Inlet vessel 12 Lower outlet end 14 Upper inlet end 16 Electrode 18 Separation vessel 20 Upper oil outlet end 22 Lower water outlet end 24 Inlet passageway 26 Inlet flange fitting 28 Outlet flange fitting 30 Pipe outlet fitting 32 Inlet longitudinal axis 34 Separation vessel longitudinal axis 36 Water collection portion 38 Water level 40 Water level control 42 Oil collection portion 44 Voltage source 46 Conductor 48 Conductor 50 Insulator 52 Water inlet 54 Water treatment process vessel 56 Oil outlet 58 Oil treatment process vessel 60 Second electrode 62 Inlet manifold 64 First separation system 66 Second separation system 68 Outlet manifold 70 Gas outlet 72 Piping 74 First separation system 76 Second separation system 78 Third separation system 80 T-fitting 82 Wash water inlet 84 Outlet 86 Mixing valve 88 Inlet 90 Desalter vessel 92 Water outlet 94 Oil outlet 96 Inlet 98 Preliminary separator 100 Gas outlet 102 Valve 104 3 phase voltage 106 Rectifier 108 DC Bus 110 Modulator 112 Conductors 114 Chopper 116 Primary 118 Transformer 120 Secondary 122 Ground 124 Conductor 124 Horizontal transition vessel 128 Tee fitting 130 First separation system/vessel 132 Second separation system/vessel 134 Baffle 136 Degassifier or pretreatment unit 138 Water collection portion 140 Third separation system/vessel 142 Dry oil path 144 Medium oil path

The basic concept of the invention is illustrated in its simplest embodiment in FIG. 1. Basically the invention includes an elongated inlet vessel 10 having a lower outlet end 12 and an upper inlet end 14. Positioned within inlet vessel 10 is an electrode 16 that provides an electrostatic field through which inlet liquid, identified in FIG. 1 as “feed”, flows. In FIG. 1 electrode 16, shown in dotted outline, is positioned within vessel 10 in which the vessel 10 is of conductive material, that is metal, so that the electrostatic field is established between electrode 16 and the wall of vessel 10.

Inlet vessel 10 is elongated, that is, it has a length measured from the upper inlet end 14 to the lower outlet end 12 that is a multiple of the largest vessel cross-sectional dimension. In the illustrated arrangement of FIG. 1 the inlet vessel 10 is in the form of a pipe, that is, a vessel that, in cross-section, is round. The length of vessel 10 should preferably be about twice the vessel diameter, however the precise length is not a critical essence of the invention except that it is important that the vessel 10 be elongated so that fluid flowing therethrough is exposed for a minimum length of time to the electrostatic field established by electrode 16.

A second basic element of the apparatus of FIG. 1 is a separation vessel 18. Vessel 18 has an upper oil outlet end 20 and a lower water outlet end 22. Further, separation vessel 18 has an intermediate inlet passageway 24 that communicates with the inlet vessel lower outlet end 12.

As the invention is illustrated in FIG. 1, an inlet flange fitting 26 is secured to the upper inlet end of inlet vessel 10 and a similar outlet flange fitting 28 is secured to the upper oil outlet end 20 of separation vessel 18. Flange fittings 26 and 28 provide convenient devices for connecting the system of FIG. 1 to piping but are not otherwise involved in the performance of the system. In like manner, the lower water outlet end 22 of separation vessel 18 is provided with a pipe fitting 30 by which water separated by the system may be carried away for disposal or further treatment.

In the embodiment of the invention as revealed in FIG. 1, a mixture of oil and water, designated as “feed” enters the system by way of inlet flange fitting 26 where it passes into inlet vessel 10. The mixture flows through the elongated inlet vessel that is preferably downwardly sloped as indicated. Sloping the inlet vessel helps allow a high liquid flux past the electrodes. Within the inlet vessel the mixture is exposed to an electrostatic field. If electrode 16 within the inlet vessel is covered with insulation then electricity is not directly conducted from the electrode 16 to the mixture but instead only an electrostatic field is maintained within vessel 10 to which the mixture is exposed. By the use of an insulated electrode 16 the voltage between the electrode and the wall of vessel 10 can be significant so that an electrostatic field is applied to the inlet mixture. The electrostatic field causes water droplets within the mixture to rapidly coalesce. The mixture, with a significant portion of the water therein coalesced into large droplets immediately passes directly into separator vessel 18 that preferably is at an angle perpendicular to the longitudinal axis of inlet vessel 10. In FIG. 1 the longitudinal axis of inlet vessel 10 is indicated by the numeral 32 while the longitudinal axis of separation vessel 18 is indicated by the numeral 34.

The mixture having been subjected to an electrostatic field and therefore having passed through an environment in which the water is rapidly coalesced enters perpendicularly into separation vessel 18. Within separation vessel 18 the inwardly flowing mixture is offered an immediate opportunity to separate into heavier and lighter components. The heavier component separates from the mixture and flows downwardly within the sloped separation vessel 18 into a water collection portion 36 which is the portion of vessel 18 below inlet passageway 24. Water within water collection portion 36 is maintained at a selected level 38 by means of a water level control 40. The water level control 40 is illustrated diagrammatically since such devices are frequently and customarily used in oil/water separation and are well known to any practitioner in the art. A typical water level control system is illustrated in and will subsequently be described with reference to FIG. 8. Basically, the water level control 40 operates a valve (not seen) connected to the pipe fitting 30 to drain water as it accumulates within the vessel lower portion 36 so that the level 38 stays at a pre-selected height within water collection portion 36.

The mixture flowing out of inlet vessel 10 through lower outlet end 12 separates and the lighter component is carried upwardly into an oil collection portion 42 of separation vessel 18. The oil component of the feed mixture having at least a substantial portion of the water extracted therefrom flows through upper oil outlet end 20 of inlet vessel 10 and through outlet flange fitting 28 for transportation to a pipeline where it may be moved to a refinery, or is conveyed to a facility for storage or further processing.

The system for separating water from a water-in-oil mixture of FIG. 1 is of ultimate simplicity compared to most oil/water separation equipment in use today and yet is arranged to provide improved performance. Specifically, a unique aspect of the separation system of FIG. 1 is that an oil/water mixture is subjected to an electrostatic field and immediately thereafter passes for separation with the water component flowing in one direction and the oil component flowing in an opposite direction. Further, the sloped arrangements of inlet vessel 10 and separation vessel 18 provide immediate gravity-assisted separation of a water-in-oil mixture after exposure to an electrostatic field. The apparatus of FIG. 1 provides the most immediate and effective separation of oil and water in the simplest possible flow arrangement as compared with other known systems.

In FIG. 1 the rudiments of the method of applying an electrostatic field to the mixture within inlet vessel 10 is illustrated. A voltage source 44 provides a voltage output between conductors 46 and 48. Conductor 48 is secured to the sidewall of inlet vessel 10 while conductor 46 is fed through an insulator 50 that extends through the sidewall of vessel 10 to electrode 16. Voltage across conductors 46 and 48 may be an AC voltage, a DC voltage, a pulsing DC voltage or a dual frequency voltage. The particular voltage applied to create an electrostatic field within the inlet vessel is not a critical element of the invention since much work has been done to define the advantages and disadvantages of various voltage systems used to augment coalescence of water in a water-in-oil mixture. As an example, U.S. Pat. No. 6,860,979 teaches a dual frequency electrostatic coalescence system that may be applied to the apparatus of FIG. 1. Such a dual frequency system is better illustrated and will be discussed with reference to FIG. 6.

The basic system of the invention illustrated in FIG. 1 is susceptible of a variety of modifications. FIG. 2 shows one example of a modification of FIG. 1 in which the inlet vessel 10, lower outlet 12, upper inlet 14, and electrode 16 all have the same element number and same purpose as described with reference to FIG. 1.

Inlet vessel lower end 12 is connected in a straight line with a water collection portion 36A that has a water level control 40 to maintain a water level 38 as described with reference to FIG. 1. The lower water outlet end 22 of the water collection portion in FIG. 2 connects to the inlet 52 of a water treatment process vessel 54 that is illustrative of any system that provides for treating and/or disposing of water extracted from the inlet mixture. The water treatment process 54 may include simply a disposal of the water extracted from the inlet water/oil mixture or it may represent further treatment to remove any residuary oil carried over from the inlet mixture, such as a hydrocyclone, a centrifugal force separator, a gravity separator, a corrugated plate separator, a flotation cell or a filter.

In the arrangement of FIG. 2 the inlet mixture flowing into the system through inlet flange 26 is subjected to an electric field provided by electrode 16 that functions to cause the water portion of the inlet mixture to coalesce. The coalesced water continues to flow downwardly into water collection portion 36A. Oil that separates out of the mixture and therefore that remains above the water level 38 turns upwardly and flows into oil collection portion 42A. Separated oil flows out of the collection portion 42A through upper oil outlet end 20 and through an oil outlet 56 into an oil treatment process area indicated by vessel 58. Oil treatment process vessel 58 is emblematic of any system for further handling, transports, treatment or storage of oil separated by the system of FIG. 2. Typically the oil treatment process 58 can be a storage facility where crude oil having a substantial portion of the water extracted therefrom is stored prior to being transported for further use, such as to a refinery for processing.

Comparing FIG. 2 with FIG. 1 shows two distinct differences. First, FIG. 2 illustrates water treatment process vessel 54 and oil treatment vessel 58 as emblematic of further treatment of separated oil and water exiting from the systems. Second, FIG. 2 compared to FIG. 1 shows a different geometrical arrangement of the flow paths of oil and water that have been separated from an inlet oil-in-water mixture. In both FIG. 1 and FIG. 2 separated oil changes directions and moves upwardly at an angle relative to the flow path of the inlet mixture. However, in FIG. 2, compared to FIG. 1, separated water continues in the same flow path of the inlet vessel. Irrespective of these differences the basic function of the systems of FIGS. 1 and 2 is the same. That is, an inlet mixture of oil-in-water flows in a downward direction through an elongated inlet vessel during which time it is subjected to an electrostatic field and a separation vessel has an inlet passageway in communication with the inlet vessel lower outlet end. FIG. 2 shows an arrangement wherein an inlet mixture of oil-in-water is subject to an electrostatic field and immediately thereafter separate passageways are provided by which the separated water and oil flows in different directions.

FIG. 3 shows another alternate embodiment of the system of this invention. In FIG. 3 inlet vessel 10 is elongated and downwardly sloped, the same as shown in FIGS. 1 and 2. However, in FIG. 3 the oil collection portion 42B is vertically upward. The longitudinal axis 32 intersects the separation vessel longitudinal axis 34 at an angle of about 45°. In FIG. 3 the mixture after having passed through the electrostatic field established by electrode 16 within inlet vessel 10 turns and enters horizontally into oil collection portion 42B that is in vertical alignment with water collection portion 36B. Separated water from the mixture coalesced by action of the electrode 16 immediately turns downwardly into the water collection portion 36B and the separated lighter oil component immediately turns upwardly into oil collection portion 42B and flows out upper oil outlet 20. Thus as with FIGS. 1 and 2, the inlet mixture is subjected to an electrostatic field and immediately thereafter the flow from the inlet mixture enters a divergent path in which separated water can flow in a direction divergent from the separated oil. In the case of FIG. 3 the separated water component immediately diverges into a downward path into water collection portion 36B while the separated oil component flows in the opposite direction, that is, upwardly into oil collection portion 42. Thus, FIG. 3 provides the same unique concept as FIGS. 1 and 2, that is, a mixture inlet through an elongated vessel in which the mixture is subject to an electrostatic field followed immediately by divergent flow pathways for the separated water and oil components.

FIG. 9 shows another alternate embodiment of the system of this invention. The inlet vessel 10, lower outlet 12, upper inlet 14, and electrode 16 all have the same element number and same purpose as described with reference to FIGS. 1, 2 and 3. Inlet vessel 10 is elongated and downwardly sloped but with flange fitting 26 oriented to receive a vertical feed. Both the water collection portion 36C and the oil collection portion 42C of the separator vessel 18 are aligned along the separation vessel longitudinal axis 34 and oriented at an angle of about 22.5° relative to the horizontal. The inlet vessel longitudinal axis 32 is perpendicular to the separation vessel longitudinal axis 34. The mixture separates, after having passed through the electrostatic field established by electrode 16 within inlet vessel 10, and the separated water turns angularly downward into the water collection portion 36C and the separated lighter oil component turns angularly upward into the oil collection portion 42C and flows out upper oil outlet 20. The outlet flange fitting 28 is oriented such that it can connect to a vertically oriented oil treatment process area. Thus as with FIGS. 1, 2 and 3 the inlet mixture is subjected to an electrostatic field and immediately thereafter the flow from the inlet mixture enters a divergent path in which separated water can flow in a direction divergent from the separated oil. As suggested by FIGS. 1, 2, 3 and 9, the angle of inlet vessel 10 can range from 0° to 45° relative to vertical and the angle of the separation vessel 18 can range from 0° to 45° relative to horizontal.

FIGS. 1, 2, 3 and 9 each make use of plural electrostatic fields. In each of FIGS. 1, 2, 3 and 9, in addition to electrode 16 positioned within the inlet vessel 10, a second electrode 60 is positioned within the oil collection portion 42, that is, there is a second electrode 60 within oil collection portion 42 of FIG. 1, within oil collection 42A of FIG. 2, within oil collection 42B of FIG. 3, and within oil collection 42C of FIG. 9. Each of the second electrodes provide electrostatic fields in the same way as the primary electrode 16 in each embodiment and serves to further aid in the coalescence of any water remaining in the separated oil after first separation has taken place. The secondary electrodes 60 may be insulated or if the percentage of water remaining in the mixture within the oil collection portion of the apparatus has diminished sufficiently then the secondary electrodes 60 may be bare electrodes operating at lower voltages.

FIG. 4 shows how the basic separation system of this invention may be used in series to more completely separate water from a water-in-oil mixture. FIG. 4 shows an inlet manifold 62 by which a water-in-oil mixture is fed into a first separation system generally indicated by the numeral 64 that has the components with the same numerical identification as FIG. 1. Outlet flange 28 of first separation system 64 connects to an inlet flange 26A of a second separation system 66. The outlet flange 28A of separation system 66 communicates with an outlet manifold 68 whereby the oil component of the mixture that flows in inlet manifold 62 is collected. Thus the first separation system 64 and second separation system 66 each function identically as has been described with reference to FIG. 1 in that each has an inlet vessel 10, a water collection portion 36 and an oil collection portion 42. Each inlet vessel has an electrode 16 and each water collection portion 36 has a pipe fitting by which water separated from the feed mixture is conveyed away from the separation system. Further, there is a second electrode 60 in both separation systems 64 and 66.

One difference in FIG. 4 compared to FIG. 1 is that a gas outlet is illustrated in communication with each of the inlet vessels 10 and 10A. Each gas outlet 70 and 70A is connected by piping 72 by which gas separated from the system can be carried away, such as to a gas collection facility, a flare or so forth.

FIG. 7 is a diagrammatic illustration of how the separation system of FIG. 2 can be connected in series. FIG. 7 diagrammatically shows a separation system 74 that functions as illustrated and described with reference to FIG. 2 and identical separation systems 76 and 78 connected in series. This is illustrative of the fact that separation systems as described herein may be connected in series with as many as necessary substantially identical separation systems connected in series to achieve the level of separation required.

Referring back to FIG. 4, this view suggests that the separation systems of this invention can easily be placed in parallel. FIG. 4 shows two separation systems 64 and 66 extending in series from an inlet manifold 62 to an outlet manifold 68. It is easy to see that any number of the systems illustrated in FIG. 4 can be placed side-by-side, in parallel, each extending from inlet manifold 62 to outlet manifold 68. In like manner the system of FIG. 7 could easily be placed in parallel with as many separation systems as required according to the volume of a water-in-oil mixture to be treated.

FIG. 5 illustrates how a separation system of this invention may be employed in a desalter system. In FIG. 5 a first separation system 64 as is described with reference to FIG. 1 functions to provide separated oil at outlet flange fitting 28 that is connected to a T-fitting 80 having a wash water inlet 82. The separated oil flowing from outlet flange 28 mixes with wash water in T-fitting 80, and the mixture passes out of the T-fitting through outlet 84, through a mixing valve 86 and through an inlet 88 pipe to a desalter vessel 90. In vessel 90 a quiet zone is provided allowing the oil and water to separate. The water introduced through wash water inlet 82 absorbs salt content in the oil discharged from first separator system 64. From desalter vessel 90 water passes out through outlet 92 and oil having substantially all the water and substantially all the salt removed therefrom flows out through oil outlet 94.

The basic concepts of the desalter of FIG. 5 are known, that is the step of using wash water to mix with oil having salt therein is known and is not the essence of the invention. The significance of FIG. 5 is that it shows how a separation system 64 of this invention can be used in a desalter to improve the efficiency and effectiveness of the desalter system.

FIG. 6 shows a further illustration of how the separation systems of this invention may be used in a desalting arrangement. A first separation system 64, as illustrated and described with reference to FIG. 1, provides separated oil through outlet flange 24 into a T-fitting 80 having a water inlet 82 as described in FIG. 5. The mixture passes through mixing valve 86 as described and into another inlet flange fitting 26 of a second separation system 66 that again is the same as the basic separation system of FIG. 1. The separated oil flowing through outlet fitting 28A enters a desalter vessel 90 where the water and oil components of the mixture separate by gravitation with the water having dissolved salt therein and relatively salt-free oil passing upwardly and out of the desalter through oil outlet 94.

FIG. 6 shows more details of circuitry by which a voltage may be applied to an electrode within a separation system to which reference will be made subsequently.

FIG. 8 shows one way in which separation systems of this invention can be added in series. In FIG. 8 an oil/water mixture enters through an inlet 96 into a preliminary separator 98 that is in the form of a vertical vessel having a gas outlet 100 at the top. Liquid passes downwardly in preliminary separator 98 with easily separated water component settling to the bottom into a water level 38 maintained by a water level control 40. The control 40 operates a water discharge valve 102 so that the level 38 is maintained within vessel 98. A pipe outlet fitting 30 provides for conveying water away from preliminary separator 98. The mixture having gas and easily separated water removed therefrom flows into a first separator system 74 like that described in FIG. 2.

As water is separated from the oil content of the mixture within separation system 74 it flows downwardly into water collection portion 36A and ultimately is drained out pipe outlet fitting 30. Oil from the mixture moves upwardly through oil collection portion 42 where it is again exposed to an electrostatic field by second electrode 60. The separated oil moves through oil outlet 56 and into a second separation system 64 and through downwardly inclined inlet vessel 10 having an electrode 16 therein. In the separation system 64 the mixture is treated as has been described with reference to FIG. 1, that is, in a basic separation system of this invention. From inlet vessel 10, the mixture, after being subjected to the electrostatic field provided by electrode 16, flows into separation vessel 18, the water being channeled downwardly into the water collection portion 36 where it mixes with water draining out of water collection portions 36A of separation system 74 and passes out of the system through a pipe outlet 30. The oil passing out of inlet vessel 10 is channeled upwardly through oil collection portion 42 and out through outlet flange fitting 28, all in the manner as described with reference to FIG. 1.

FIG. 8 is an illustration of how the unique separation system of this invention lends itself to a variety of combinations, all achieved with the basic concepts as revealed in FIG. 1. In the system of FIG. 8 the mixture is subjected to electrostatic field provided by four (4) electrodes. To achieve highly effective separation of water from the oil contained in the mixture, the strength of the electrostatic field of successive electrodes can be increased since each is in a portion of the system wherein the water content of the mixture has been reduced. As an example, while electrodes 16 and 60 of separation system 74 may be insulated, electrodes 16 and 60 of separation system 64 may be uninsulated, that is bare. Additionally, as shown by FIGS. 10, 11 and 12, different electrode configurations may be used for electrodes 16 and 60 in order to achieve the desired electrostatic field. For example, in FIG. 10 electrodes 16A are in the form of parallel plates. In FIG. 11 the electrodes 16B are in the form of concentric cylindrical members 16B, while in FIG. 12 a coaxial electrode 16C is in the shape of a rod surrounded by a concentric cylindrical member 16D. Second electrode 60 may have any of the cross-sectional arrangements shown in FIGS. 10, 11 and 12.

As mentioned with reference to FIG. 1, each of the electrodes employed in the separation systems described herein is supplied by a voltage potential which may be an AC voltage, a DC voltage, a rectified AC voltage or an AC voltage having selected frequencies and wave forms. An effective voltage format for use with the electrostatic separator systems of this invention is a dual frequency voltage as described in detail in U.S. Pat. No. 6,860,979 entitled “Dual Frequency Electrostatic Coalescence.” This patent issued on May 1, 2005, and is incorporated herein by reference. FIG. 6 shows a basic circuit revealed in this patent by which a dual frequency voltage is applied to electrode 16 of separation system 64. In this dual frequency circuit a three-phase voltage source 104 is applied to a rectifier 106 to produce a voltage on a DC bus 108. Voltage from DC bus 108 supplies a modulator 110 that, by signals fed on conductors 112, controls a chopper 114 that provides an AC voltage of selectable frequency to the primary 116 of a transformer 118. The secondary 120 of transformer 118 applies voltage between ground 122 and a conductor 124 that supply voltage passing through insulator 50 to electrode 16. The circuit of FIG. 6 provides a method of augmenting the separation of the oil and water components of a mixture flowing through inlet vessel 10 by providing an AC voltage source of a readily selectable frequency F1 that is modulated in intensity at a selected frequency F2.

FIG. 13 illustrates an alternate embodiment of the invention as compared to the basic embodiment of FIG. 1. In FIG. 13 a horizontal transition vessel 126, typically in the form, as illustrated, of a length of pipe, interconnects oil collection vessel 42 with inlet vessel 10. A tee fitting 128, extends from the bottom of horizontal transition vessel 126 and connects to the inlet of water collection vessel 36. Thus water separating in inlet vessel 10 and oil collection vessel 42 settles to the bottom of horizontal transition vessel 126 and drains out through tee fitting 128 into water collection vessel 36 while encountering reduced turbulence.

In the drawings the basic configurations of the separator of this invention is illustrated in FIGS. 1, 2, 3, 9 and 13. Different systems by which this separator system can be applied are illustrated in FIGS. 4, 5, 6, 7 and 8. FIGS. 5 and 6 illustrate specifically how the separator system herein can be employed in a desalting system in which wash water is utilized. It is important to emphasize that the illustrations of how the separator system of this invention can be modified into various configurations, as exemplified in FIGS. 4 through 8, are examples only and by no means are illustrated as the only arrangements by which the separator system can be employed.

Referring now to FIG. 14, a first separation vessel 130 and a second separation vessel 132 are arranged one above the other, each vessel 130 being an upflow leg or stage that has the wet oil inlet 14 located below the electrode 16 but above the water level control 40 (and therefore above the water level 38). The orientation of the vessels 130, 132 may vary from vertical to horizontal (see FIGS. 15 to 15B) relative to one another. A vertical orientation has logistical advantages and a horizontal orientation has fluid flow advantages. Varying between the two orientations blends the advantages of both orientations.

As the wet oil enters through inlet 14 of the first vessel 130 below the electrode 16, the wet oil is substantially immediately affected by the electric field. The largest water droplets coalesce and flow downward into the water collection portion 26 before the wet oil encounters the electrode 16. The angle of the vessel 130 relative to horizontal (see e.g., FIG. 15) allows the expedited countercurrent removal of the coalesced water to the water collection portion 26. As the drier oil flows upward to the oil collection portion 42 of the vessel 130, smaller water droplets coalesce and separate into the countercurrent flow. The drier oil passes from the outlet 20 of the first vessel 130 and enters the inlet 14 of second vessel 132 below the electrode 16, where the above separation process is repeated. Each vessel 130, 132 is equipped with a gas outlet 70 by which gas separated from the system can be carried away, such as to a gas collection facility, a flare or so forth.

A plurality of baffles 134 that are arranged parallel to one another may be provided in the water collection portion 26 of each vessel 130, 132. The baffles 134, which are preferably oriented parallel to the axis of the vessel 130, 132 may be vertical, horizontal, or angled baffles (see FIGS. 19 to 21). A vertical baffle decreases the Reynolds Number and, therefore, system turbulence. A horizontal baffle decreases the Reynolds Number and settling distance. However, a horizontal configuration increases the number of surfaces on which sand may accumulate. Additionally, the separated oil droplets must cross the water flow in order to travel upward and recombine with the continuous oil phase. An angled baffle—that is, a baffle oriented between 0 and 90 degrees—has the potential to combine the advantages of vertical and horizontal baffles, providing shorter settling distances and an increased angle of repose for the sand. The separated oil droplets cross the water flow at the wall where flow velocity is a minimum.

As illustrated in FIGS. 16, 18, and 24A & B a degasser or pretreatment unit 136 may be connected to the inlet 14 of the first separator vessel 130. Pretreatment prevents excessive gas from entering into vessel 130 (and 132) and reduces the inlet water volume by initiating water removal. In a preferred embodiment, the pretreatment unit 136 is a PORTA-TEST WHIRLYSCRUB® V™ vertical centrifugal separator (Cameron Corp. Process Systems, formerly National Tank Company Corp., Houston, Tex.) or CONSEPT ICD™ centrifugal separator (also Cameron Corp. Process Systems, formerly National Tank Company Corp., Houston, Tex.). The tangential inlet on these particular centrifugal separators promotes free-gas removal and initiates free-water coalescence by creating a high-g environment. As illustrated in FIGS. 24A & B, pretreatment unit 136 may include a water collection portion 138.

Experiments by the inventors on various configurations of a compact electrostatic separator made according to this invention have provided insights into what works best. Different performance characteristics depend on whether the oil-water flow is upward or downward. For example, the oil-water flow in the arrangement of FIGS. 24A & B is a downward flow in each of the separator vessels, 130, 132 (with the pretreatment unit 136 and vessels 130, 132 being connected to a single header in FIG. 24B and controlled by a single level control). With respect to inlet water fraction, for high water fractions (about 30-70% BS&W), up flow yields superior results whereas for moderate water fractions (about 5-10% BS&W) down flow performs better. With respect to outlet water fractions, the up flow configuration has a limit on the amount of water that can be removed. The drag of the upward flowing oil prevents small amounts of water from falling into the water collection portion 36 of the vessel 130, 132, and this configuration can dry oil only to moderate fractions. However, with moderate inlet water fractions, a down flow configuration can yield oil with a low (<1%) water fraction.

With respect to the electrostatic technique, AC is the only appropriate technique in up flow configurations given very wet oil inlet flows. Furthermore, the electrode 16 is preferably a bare electrode when the wet oil has a high water fraction. Because the flow coming into a down flow configuration is moderately wet, there is a possibility to use AC as well as dual polarity and dual frequency techniques to achieve very dry outlet oils. As discussed previously in connection with FIG. 6, an effective voltage format for use with the electrostatic separator systems of this invention is a dual frequency voltage as described in detail in U.S. Pat. No. 6,860,979 entitled “Dual Frequency Electrostatic Coalescence” and incorporated herein by reference. The moderately wet inflow also provides an opportunity to use an insulated electrode 16.

Referring now to FIGS. 22 and 23, a compact electrostatic separator is illustrated that combines the most advantageous features of an up flow and a down flow configuration. Wet oil enters the inlet 14 of a first separator vessel 130, which is in an up flow configuration, below the electrode 16 and above the water level control 40. Because of the high water fraction of the wet oil, first stage electrode 16 is a bare electrode used in combination with AC technology. Electrode 16 causes water droplets to coalesce and fall out of the oil-water mixture into the water collection portion 36. Because of the high density of the water relative to the oil and its low viscosity, most of the water can fall out of the mixture into the water collection portion 36. However, at some point, the drag force of the upwardly moving oil-water mixture exceeds the remaining water's ability to move downward. With much of the water exiting the lower water outlet end 22 of the first vessel 130, a moderately dry oil exits the upper oil outlet end 20 of vessel 130 and enters the inlet 14 to a second separator vessel 132, which is in a down flow configuration.

The moderately dry oil enters the second vessel 132 about even with the electrode 60. Second stage electrode 60 performs the same function as that of the first stage electrode 16. Electrode 60 may be an insulated electrode and used in combination with AC or with dual polarity and dual frequency techniques. With the momentum of the water and the mixture being in the same direction, the drag on the oil-water mixture is reduced and much more of the remaining water can fall out into the water collection portion 36 of the second vessel 132. This water exits at the lower water outlet end 22 and nearly dry oil exits from the upper oil outlet end 20. Note that because upper oil outlet end 20 of the first vessel 130 and the inlet 14 of the second vessel 132 are both at the upper ends of the vessels 130, 132, this configuration occupies less space than the systems illustrated, for example, in FIGS. 14 and 15.

Laboratory studies demonstrate that the addition for reactance to the transformer 118 (see FIG. 6) is beneficial. From preliminary lab data, when the reactance is absorbing about 5 to 70% of the input voltage, it is performing two functions. First, it limits both the number and length of arcing short circuits. This tends to increase the applied voltage on the electrode 16 and produce more coalescence. Second, the voltage adjustments caused by the arc response induce a voltage modulation. This voltage modulation enhances the coalescence of water droplets of varying size, which leads to improved separation. The combination of these two properties improves the quality of both the oil and water (see Tables 1 and 2).

TABLE 1 Effect of Added Reactance on the Quality of Oil and Water. 2000 Volts 1st Electrode; 5000 Volts 2nd Electrode ~100° F. 2000 B/D psf, 32-34% H₂O PPM Oil % Oil Added 1st 2nd Amps Amps Reactance % H₂O Dry Angle of Water Water 1st 2nd MHY Oil Out Baffle Outlet Outlet 1.4 0.4 0 5.6* 0 160 36*   1.4 0.4 0 5.6* 45 179 36*   1.4 0.4 0 5.6* 90 261 36*   0.5 0.4 35 5.2 45 58 1.7 0.5 0.4 47 5.6 45 123 2.7 0.5 0.4 59 5.5 45 120 2.3 0.6† 0.6 59 4.9 45 94 0.5 *Values averaged †One sample only 3000 Volts and 7500 Volts

TABLE 2 Effect of Added Reactance and No Baffles in the Second Separator Vessel on the Quality of Oil and Water. ~100° F. 2000 B/D psf, 32-34% H₂O PPM Oil PPM Oil Added % H₂O 1st Water 2nd Water Amps KVoltage Amps KVoltage Reactance Dry Oil Angle of Outlet Outlet 1st In/Out 2nd In/Out MHY Out Baffle Baffled Not Baffled 0.6 4.0/1.7 0.6 8.0/7.6 56 5 45 49 10K 0.6 4.0/1.7 0.9 9.1/8.2 56 4.6 45 57  5K 0.6 4.0/1.7 1.3 11.0/9.1  56 4.3 45 51 220  

Referring now to FIGS. 25 and 26, an additional oil outlet 20 a is provided that routes oil dry enough to meet a user's requirements on a dry oil path 142 that bypasses the second separator vessel 132. In FIG. 25, wet oil (about 30-70% H₂O) enters inlet 14 ₍₁₎ of the first separator vessel 130 and dry oil (about <1% H₂O) exits at the top end of the vessel 130 through outlet 20 a. The balance of the medium-wet or moderately dry oil (about 5-10% H₂O) exits outlet 20 _(B) and enters the inlet 14 ₍₂₎ of the second separator vessel 132. Dry oil then exits the second vessel 132 through outlet 20 _(D) and along dry oil path 142. Preferably, the flow through outlet 20 _(A) is controlled to ensure that any oil that exceeds the user's requirements is not routed through the outlet 20 _(A) (thereby bypassing the second vessel 132). The same holds true for outlet 20 _(D).

In FIG. 26, the first separator vessel 130, which is an up flow vessel, includes two additional outlets 20 _(A) and 20 _(B). Preferably, outlet 20 _(B) is located in close proximity to the wet oil inlet 14. As wet oil passes through inlet 14 ₍₁₎ and enters the first separator vessel 130, a portion of the wet oil is diverted to outlet 20 _(B) and into inlet 14 ₍₂₎ of the second separator vessel 132, which is also an up flow vessel. Dry oil that meets the user's requirements exits through additional outlet 20 _(A) located at the top end of vessel 130 and travels along path 142.

The second separator vessel 132 converts the wet oil from the first vessel 130 to a medium-wet oil, which exits the second vessel 132 through outlet 20 _(D) and travels along medium-wet oil path 144 to the inlet 14 _((3B)) of an additional or third separator vessel 140. Vessel 240 is a down flow vessel substantially similar in structure to that of vessels 130, 132 as illustrated in, for example, FIGS. 24A & B. Medium- or moderately wet oil which passes through outlet 20 _(C) of the first vessel 130 also travels along medium-wet oil path 144 to the inlet 14 _((3A)) of a third vessel 140. Dry oil then exits through outlet 20 _(E) of the third vessel 140 and travels along dry oil path 142.

While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification, but is to be limited only by the scope of the attached claims, including the full range of equivalency to which each element thereof is entitled. 

What is claimed is:
 1. A method of separating water from a water-and-oil mixture, the method comprising the steps of: (a) flowing a water-and-oil mixture into an inlet of a first elongated separator vessel, the first elongated separator vessel being oriented on an incline and having an electrode located toward its upper end; (b) passing the water-and-oil mixture through an electric field of the first elongated separator vessel whereby water in the water-and-oil mixture coalesces and a first water predominant fluid flows downward; (c) flowing a portion of a first oil predominant fluid out of an outlet of the first elongated separator vessel and into an inlet of a second elongated separator vessel, the second elongated separator vessel being oriented on an incline and having an electrode located toward its upper end; (d) passing the portion of the first oil predominant fluid through an electric field of the second elongated separator vessel whereby water in the portion of the first oil predominant fluid coalesces and a second water predominant fluid flows downward; and (e) allowing a second portion of the first oil predominant fluid to exit an outlet of the first elongated separator vessel and bypass the second elongated separator vessel.
 2. A method according to claim 1 the inlet to the first elongated separator vessel and the second elongated separator vessel is located relative to the electrode to provide for a predetermined direction of flow of the water-and-oil mixture as the water-and-oil mixture enters the separator vessel, the direction of flow being a direction of flow selected from the group consisting of an upward direction of flow and a downward direction of flow.
 3. A method according to claim 1, the portion of the first oil predominant fluid flowing out of the outlet of the first elongated separator vessel and into the inlet of the second elongated separator vessel is a portion selected from the group consisting of a wet oil portion and a medium-wet oil portion.
 4. A method according to claim 1 further comprising the step of flowing the water-and-oil mixture to a pre-separation unit prior to said step (a).
 5. A method according to claim 1, at least one of the first water predominant flow and the second water predominant flow passes through a plurality of baffles.
 6. A method according to claim 1, the electrode of the first and second elongated separator vessels is each in circuit relationship to a voltage source at a different potential than the other voltage source.
 7. A method of separating water from a water-and-oil mixture, the method comprising the steps of: (a) flowing a water-and-oil mixture into an inlet of a first elongated separator vessel, the first elongated separator vessel being oriented on an incline and having an electrode located toward its upper end; (b) passing the water-and-oil mixture through an electric field of the first elongated separator vessel whereby water in the water-and-oil mixture coalesces and a first water predominant fluid flows downward; (c) flowing a portion of a first oil predominant fluid out of an outlet of the first elongated separator vessel and into an inlet of a second elongated separator vessel, the second elongated separator vessel being oriented on an incline and having an electrode located toward its upper end; (d) passing the portion of the first oil predominant fluid through an electric field of the second elongated separator vessel whereby water in the portion of the first oil predominant fluid coalesces and a second water predominant fluid flows downward; and (e) after said step (a), allowing a portion of the water-and-oil mixture to substantially immediately exit an outlet of the first elongated separator vessel and flow into an inlet of an additional elongated separator vessel, the additional elongated separator vessel being oriented on an incline and having an electrode located toward its upper end; and (f) passing the portion of the water-and-oil mixture through an electric field of the additional elongated separator vessel whereby water in the portion of the water-and-oil mixture coalesces and a third water predominant fluid flows downward.
 8. A method according to claim 7, the inlet to the additional elongated separator vessel is located relative to the electrode to provide for a predetermined direction of flow of the water-and-oil mixture as the water-and-oil mixture enters the additional elongated separator vessel, the direction of flow being a direction of flow selected from the group consisting of an upward direction of flow and a downward direction of flow.
 9. A method according to claim 8 further comprising the step of: (g) flowing a portion of a third oil predominant fluid out of an outlet of the additional elongated separator vessel and into an inlet of the second elongated separator vessel. 